Trace metal speciation and bioavailability in urban soils

摘要

Urban soils often contain concentrations of trace metals that exceed regulatory levels. However, the threat posed by trace metals to human health and the environment is thought to be dependent on their speciation in the soil solution rather than the total con- centration. Three inactive railway yards in Montreal, Quebec, were sampled to investigate the speciation and bioavailability of Cd, Cu, Ni, Pb and Zn. Soil solutions were obtained by centrifuging saturated soil pastes. In the soil solutions, up to 59 of the dis- solved Cd was in its free ionic form. For Cu, Pb and Zn, organic complexes were the predominant species. Over 40 of Ni was present as inorganic complexes if the solution pH exceeded 8.1. Multiple regression analyses showed that pH and total metals in soi1 were significantly correlated with the activities of free metal ions, except for Cd~(2+), which only had a weak correlation with soil pH. Free, dissolved and total soil metals were tested for their ability to predict metal uptake by plants in the field. However, none of these metal pools were satisfactory predictors. The results indicated that in these urban soils, trace metals were mainly in stable forms and bioavailability was extremely low.